2009 Yamaha grizzly 450 4 x 4 utility four wheeler

Hi new here having carburetor problems with my o nine grizzly hard starting sometimes won’t start if it does start you can’t touch the throttle or it will stall then out of the blue it runs fine does anyone have any suggestions has anyone changed the pilot jet for this problem i’ve rebuilt and cleaned carburetor and jets three times out of ideas please help!